A person may claim defamation by a literary or dramatic work intended as fictional if the characters in the work resemble actual persons so closely that it is reasonable for readers or viewers to believe that the character is intended to portray the person in question. A disclaimer that the work is fiction and does not depict any persons living or dead will not automatically foreclose a defamation claim, but it is still a good idea and may be used as evidence as to whether readers or viewers would be reasonable in concluding that it is a depiction of the plaintiff.
What is a Defamatory Statement
A defamatory statement is a false statement of fact that exposes a person to hatred, ridicule, or contempt, causes him to be shunned, or injures him in his business or trade. Statements that are merely offensive are not defamatory (e.g., a statement that Bill smells badly would not be sufficient (and would likely be an opinion anyway)). Courts generally examine the full context of a statement's publication when making this determination.
In rare cases, a plaintiff can be “libel-proof”, meaning he or she has a reputation so tarnished that it couldn’t be brought any lower, even by the publication of false statements of fact. In most jurisdictions, as a matter of law, a dead person has no legally-protected reputation and cannot be defamed.
Defamatory statements that disparage a company's goods or services are called trade libel. Trade libel protects property rights, not reputations. While you can't damage a company’s "reputation," you can damage the company by disparaging its goods or services.